This invention relates to lasers and more particularly to apparatus for and a method of extracting an output beam from a laser system which utilizes a phase conjugate mirror.
The marriage of phase conjugation to a laser system is a recent phenomenon in the field of nonlinear optics and laser physics. A detailed analysis and description of this phenomenon is presented in an article entitled "THROUGH THE LOOKING GLASS WITH PHASE CONJUGATION" by Feldman et al., in Los Alamos Science (Fall 1982). The phase conjugate mirror may be used with significant advantage in a master oscillator power amplifier system in which the output of the oscillator is amplified by a double pass through highly pumped laser rods utilizing reflection from such a mirror. The advantage is that the phase conjugate mirror eliminates phase distortions in the beam caused primarily by the amplifier and thus enhances the quality of the reflected beam even when amplified to high energy levels and pulsed at high pulse repetition rates. With a conventional mirror, such phase distortions remain in the beam output from the system.
Another property or characteristic of the phase conjugate mirror is its capability of reflecting the conjugate of the laser beam incident upon it such that the conjugate beam travels along the same path as the incident beam regardless of the angle of incidence. This introduces a problem of extracting the beam output from the system without permitting the conjugate beam or even part of it to propagate back into the master oscillator and damage it. A beam splitter in the path of the conjugate beam will divert some of the latter as a useful output but the undiverted portion that propagates through the beam splitter passes into the oscillator and may damage it. This occurs even with coated beamsplitters because of the inefficiencies of such coatings and the amplified level of the conjugate beam.
This invention is directed to a solution to this problem.